My first thought was about scabies and not ringworm, but it is best to get it diagnosed by a vet. If it is scabies, it is nothing to take lightly. Like CAB said, it used to be ( and may still be) a disease that is reportable which will lead to herd quarantine. By before you get all excited, have it checked out. It may not be this at all.
If it is only on your white animals or on the white markings on red animals, it could be a disease that is caused by an allergic reaction to sunlight. I have only seen this twice in my life. Several years ago, a neighbor had this happen on his Shorthorn cows. The red parts of the animals were fine, but the white markings were blistered with ugly scabs and if you pulled them off they were raw and bloody. He had to run the cows through the chute every day and treat them and I cannot remember what was used. I had one of my donor cows get this 4 years ago, and we had to put her in total darkness for 3 weeks. It was hard to have to put her and her calf in the barn and cover all the windows and keep the doors all closed in mid June, but it did work.
It may be just ringworm as several others have suggested, but you usually do not hear of older animals getting ringworm, unless they have never been in contact with it before. I guess this is a possibility, but it is not real common.